Biogeographic patterns of marine organisms are largely a result of dispersal of early life stages. In turn, dispersal potential is directly affected by developmental mode. Marine organisms have evolved multiple diverse modes of embryonic development. Some release gametes into the water column while others brood embryos internally or encase their embryos in structures attached to the benthos. The developmental mode of any given taxon may be a result of two major factors: phylogenetic constraint and ecology (or a combination of the two). My goal is to quantify and discriminate between the impacts of these factors on developmental mode. Specifically, I plan to examine the effects of phylogenetic history, body size, trophic level, climate, available food energy, and habitat type on development. These will be evaluated in six marine gastropod families with varying developmental modes and for which species-level phylogenies are available: Muricidae, Calyptraeidae, Conidae, Littorinidae, Cypraeidae, and Turbinidae. Results from this project will illuminate the origins of the complex biogeographic patterns displayed by marine animals.